The Cardinals optioned Walker to Triple-A Memphis on Wednesday, Jeff Jones of the Belleville News-Democrat reports.
Walker is not in the lineup for Monday's game versus the Diamondbacks.
Walker is absent from the lineup for Wednesday's contest in Oakland.
Walker is not included in the starting lineup for Sunday's matchup against the Diamondbacks, John Denton of MLB.com reports.
Walker is absent from the lineup in Tuesday's game against the Phillies.
Walker isn't starting Saturday against the Dodgers, John Denton of MLB.com reports.
Walker has gone 2-for-13 with seven strikeouts and a walk over his first five Grapefruit League games.
Walker went 1-for-4 with a solo home run in Sunday's win over the Phillies.
Walker isn't in the Cardinals' lineup Saturday against Cincinnati.
Walker went 3-for-4 with a double, a home run, three runs scored and two RBI in Tuesday's 10-6 win over Atlanta.